The present invention relates to methods and apparatus for recovering useful liquid and gaseous hydrocarbons from both naturally-occurring and man-made mixtures of hydrocarbons and mineral substrates; and more particularly to methods and apparatus for processing hydrocarbon-containing geologic materials, including tar sands, oil sands, oil sandstones, oil shales, and petroleum-contaminated soils, to recover petroleum-like hydrocarbons, and especially crude oil, therefrom and to render the mineral substrate residues suitably low in hydrocrbons, acids, and bases for environmentally-acceptable disposal.
As used herein, hydrocarbonaceous deposit is to be taken to include tar sands, oil sands, oil sandstones, oil shales, and all other naturally-occurring geologic materials having hydrocarbons contained within a generally porous rock-like inorganic matrix. The matrix may be loose, friable, or indurate. Contaminated soil is to be taken to include soils which have been impregnated with hydrocarbons, as is known to occur in petroleum drilling, well operating, storage, refining, transport, and dispensing processes.
Tar sands are naturally-occurring geological formations found in, for example, Canada (Alberta). Such sands have potential for yielding large amounts of petroleum. Tar sands are porous, generally loose or friable, and typically contain substantial amounts of clay and have the interstices filled with high-viscosity hydrocarbons known generally in the art as bitumen. Most of these tar-like bituminous materials are residues remaining after lighter (lower molecular weight) hydrocarbons have escaped or have been degraded through the action of microorganisms, water washing, and possibly inorganic oxidation. Very extensive tar sand deposits occur in northern Alberta along the Athabaska River and elsewhere. Tar sand layers in this area may be more than 60 meters thick and lie near the surface over a total area of about 86,000 km2. They are estimated to contain a potential yield in excess of 1.6 trillion barrels of oil.
Oil shales are related to oil sands and tar sands; however, the substrate is a fine-grained laminated sedimentary rock typically containing an oil-yielding class of organic compounds known as kerogen. Oil shale occurs in many places around the world. Particularly kerogen-rich shales occur in the United States, in Wyoming, Colorado, and Utah, and are estimated to contain in excess of 540 billion potential barrels of oil.
Hydrocarbons recoverable from tar sands and oil shales may comprise, but are not limited to, bitumen, kerogen, asphaltenes, paraffins, alkanes, aromatics, olefins, naphthalenes, and xylenes.
In the known art of petroleum recovery from hydrocarbonaceous deposits, the high molecular weight bituminous or kerogenic material may be driven out of the sands, sandstones, or shales with heat. For example, in a known process for recovering kerogen from oil shale, crushed shale is heated to about 480xc2x0 C. to distill off the kerogen which is then hydrogenated to yield a substance closely resembling crude oil. Such a process is highly energy intensive, requiring a portion of the process output to be used for firing the retort, and thus is relatively inefficient. Also, a significant percentage of the kerogen may not be recovered, leaving the process tailings undesirable for landfill.
Another process, as disclosed in Canadian Patent Application No. CA 2177018, filed May 21, 1996 and laid open Nov. 22, 1997, requires the use of hydrogen peroxide to separate an aqueous slurry of tar sand into an upper froth layer, a middle clean water layer, and a lower clean sand layer. Released bitumen is contained in the froth layer which is recovered by decanting of the batch-process vessel. (The disclosure incorrectly refers to, and claims, hydrogen peroxide as a catalyst; the hydrogen peroxide is not a catalyst but is an oxidizing reagent which is consumed in the process.)
The disclosed process has at least two shortcomings. First, it is configured specifically as a batch method and provides no guidance in either hardware or process steps toward making it continuous, as would be highly advantageous for processing very large volumes of ore on a sustained basis. Second, it recovers bitumen from tar sand in substantially unchanged form and molecular weight.
Other known processes, for recovering bitumen from tar sands for example, require the use of caustic hot water or steam. For example, a process currently in use in Canada requires that a hot aqueous slurry of tar sand be mixed with high concentrations of aqueous caustic soda to fractionate the bitumen into lower molecular weight hydrocarbons which may then be separated from the mineral residues and refined further like crude oil. This process has several serious shortcomings. First, it is relatively inefficient, typically recovering less than about 70% of the hydrocarbons contained in the sands. xe2x80x9cFreexe2x80x9d hydrocarbons, that is, compounds mechanically or physically contained interstitially in the rock, may be recovered by this process; but xe2x80x9cboundxe2x80x9d hydrocarbons, that is, compounds electrostatically bound by non-valence charges to the surface of clays or other fines having high electronegative surface energy, are not readily released by some prior art process. In fact, high levels of caustic may actually act to inhibit the desired release of organic compounds from such surfaces and may tend to emulsify released bitumen with water, making later separation very difficult. Thus, the prior art process is wasteful in failing to recover a substantial portion of the hydrocarbon potential, and the mineral substrate residue of the process may contain substantial residual hydrocarbon, making it environmentally unacceptable for landfill. Typically, the aqueous tailings of prior art processes require ponding, sometimes for years, to permit separation of water from the suspended and entrained particles. The volumes and surface areas of such ponds in Alberta are enormous.
Second, the wet sand and clay residues can be caustic and may not be spread on the land or impounded in lagoons without extensive and expensive neutralization.
Third, the caustic aqueous residual may contain high levels of dissolved petroleum, which is non-recoverable and also toxic in landfill. Such residual also has a high Chemical Oxygen Demand (COD), making ponds containing such residual substantially anoxic and incapable of supporting plant or animal life and highly dangerous to waterfowl.
Fourth, oils recovered by the prior art process typically have high levels of entrained or suspended fine particulates which must be separated as by gravitational settling, filtration, or centrifugation before the oils may be presented for refining. These particulates may be emulsified with the oils and can be extremely difficult to separate out.
Fifth, the present-day cost of oil recovered from Albertan tar sands by prior art process may require a substantial governmental subsidy to match the world spot price of crude oil.
It is a principal object of the invention to provide an improved process for recovering hydrocarbons from hydrocarbonaceous deposits in greater than 90% yield.
It is a further object of the invention to provide an improved process for recovering hydrocarbons from hydrocarbonaceous deposits in greater than 99% yield.
It is a still further object of the invention to provide an improved recovery process which provides a substrate residue which is acceptable under applicable environmental guidelines for landfill disposal.
It is a still further object of the invention to provide an improved recovery process which can recover both free and bound hydrocarbon compounds from particulate mineral substrates and thereby recover a high percentage of all of the hydrocarbons therein.
It is a still further object of the invention to provide an improved recovery process which is substantially less expensive to operate on a per-unit of ore basis than are known treatment processes.
It is a still further object of the invention to provide an improved recovery process which can yield a refinable oil product at a unit cost competitive with that of crude oil produced conventionally from wells.
Briefly described, a hydrocarbonaceous ore mixture typically containing bitumen and/or kerogen and a mineral substrate is crushed or otherwise comminuted as needed to the consistency of wet sand. The ore may be screened to eliminate rocks or plant materials from the soil overburden of the ore deposit. The comminuted ore is mixed with water to form a slurry, preferably is heated to between about 20xc2x0 C. and about 100xc2x0 C., and is blended with an oxidant in aqueous solution, preferably hydrogen peroxide. The water may include fresh water, salt water, seawater, tailing pond water, recycled process water, and combinations thereof. The slurry is strongly agitated for between 5 and 60 minutes. Both free interstitial hydrocarbons and those hydrocarbons bound electrostatically to the surfaces of clay-like particles are released from the mineral substrate, possibly by an electrophysical reaction in the presence of the oxidant. A portion of the released bituminous and kerogenic compounds may be lysed by the oxidant in a controlled Fenton""s reaction to yield organic compounds having lowered molecular weights. Separation from the process water phase and the residual mineral phase may be enhanced by addition of flocculants to the slurry and by sparging of the slurry with microbubbles of gas. The water and rock tailings from the process are substantially free of hydrocarbon contamination and are environmentally suitable for disposal. In a preferred embodiment, the oxidant is divided and is added to the slurry at a plurality of points and times during agitation.
In a further preferred embodiment, the only wastewater from the process is the water contained in the wet tailings of sand and clay. The remainder of the separated water is recycled into the mixing stage at the head end of the process.